Acoustic Discrimination

Exploring Technology to Support Selective Fishing

A fishing vessel appears in the ocean. Text reads: Purse-seine vessels, which catch 66% of the world´s tuna, rely largely on Fish Aggregating Devices (FADs) to capture tropical tuna species. In partnership with purse-seine fleets and AZTI research institute, ISSF researchers are studying how vessels that use FADs may be able to fish more selectively by applying acoustic technology like echosounders in new ways.
A fish aggregating device (FAD) appears in the water.
A tracking buoy with echosounder fades in to the right of the FAD. The echosounder has lines radiating out from it, and casts a shadow in front of the FAD.
Aquatic life — including fish, sharks, and rays — fade in near the FAD. Most creatures fall within the shadow cast by the echosounder. It is revealed the echosounder can determine which have swim bladders, and others do not.
A fishing vessel appears in the ocean. Text reads: Purse-seine vessels, which catch 66% of the world´s tuna, rely largely on Fish Aggregating Devices (FADs) to capture tropical tuna species. In partnership with purse-seine fleets and AZTI research institute, ISSF researchers are studying how vessels that use FADs may be able to fish more selectively by applying acoustic technology like echosounders in new ways.
A fish aggregating device (FAD) appears in the water.
A tracking buoy with echosounder fades in to the right of the FAD. The echosounder has lines radiating out from it, and casts a shadow in front of the FAD.
Aquatic life — including fish, sharks, and rays — fade in near the FAD. Most creatures fall within the shadow cast by the echosounder. It is revealed the echosounder can determine which have swim bladders, and others do not.

Acoustic Data Can Help Fishers Identify Species at FADs

Tuna fishers use buoys equipped with echosounders to remotely track their FADs in the ocean. They plan fishing trips based on the buoys' acoustic estimate of the amount of fish aggregated at FADs.

But current technology does not allow for discriminating species or sizes, which means fishers may spend time and resources traveling to areas where the FADs have attracted other species or sizes they were not targeting for their catch.

Target Outcome: Knowing which species are at FADs can help a vessel's crew focus most on the FADs that are attracting a higher proportion of the target tuna species. This approach can reduce overfishing and bycatch — and also save fuel and reduce emissions from fishing operations.

One current challenge to fishing selectively is that FADs can attract a mix of tuna and other marine species as well as fish of different sizes, making it difficult to catch only the tuna species that are being targeted.

FAD tracking buoys with echosounders emit sound pulses that reflect off underwater targets like fish. Fishers rely on echosounder data to know the amount of fish that are aggregating at FADs.

Each species sends a different sound response back to echosounders — and has a distinctive acoustic signature.

As of 2022, after years of research, scientists have "decoded" the individual acoustic signatures of skipjack, bigeye, and yellowfin. These three species have contrasting frequency responses.

Species Reflect Sound Differently

Skipjack, bigeye, and yellowfin are the main tropical tuna species found at FADs. Depending on the ocean region, certain species may be suffering from overfishing. Ideally, before they make a set, fishers could target the tuna species whose stocks are at healthy levels.

The process of using echosounders to identify and differentiate species is called “acoustic discrimination.”

Tuna species produce different acoustic signatures based on the presence/sizeor absence of a swim bladder.

Swim bladder: an air-filled sac that functions as a ballast organ, enabling the fish to maintain its swim depth without floating upward or sinking.

Fish with a swim bladder, like bigeye and yellowfin tuna, reflect more sound.

Fish without a swim bladder, like skipjack tuna, reflect less sound.

Acoustic Discrimination Timeline

Through at-sea research, ISSF scientists have been studying the acoustic responses and behavior of tuna and other species in purse-seine fisheries.

Our findings may enable tuna fishers to use echosounders and other acoustic equipment to better identify the species, size, and number of tuna and non-tuna at fish aggregating devices (FADs) before they cast their nets — helping to avoid overfishing and reduce bycatch.

ISSF acoustic-discrimination research has been funded by the FAO GEF Common Oceans ABNJ Tuna Project, the Basque government, and NOAA fisheries.

Timeline Key

technology iconTechnology research iconResearch publication iconPublications
technology icon 1984
First generation of radio buoys
technology icon 1986
Second generation of radio buoys
technology icon 1996
Radio buoys with Global Positioning System (GPS)
technology icon 1999
First generation of echosounder buoys
technology icon 2006–07
Second generation of echosounder buoys
research icon 2011
Eastern Pacific Ocean ISSF research cruise on the vessel Yolanda L | Acoustic and optical surveys of aggregated tunas
Taking acoustic measurements in the cage offshore.
© ISSF 2011
technology icon 2013
Multi-frequency echosounder buoys
research icon 2014
Central Pacific Ocean ISSF research cruise on vessel Albatun Tres | Comparing echosounder measurements at different frequencies with catches at FADs
Taking acoustic measurements in the cage offshore.
Photo by Fabian Forget, © ISSF 2014
publication icon 2014
“Evolution and current state of the technology of echo-sounder buoys used by Spanish tropical tuna purse seiners in the Atlantic, Indian and Pacific Oceans” | Published in Fisheries Research
research icon 2015
Tuna target strength and frequency response research begins at sea
research icon 2016
Atlantic Ocean ISSF cruise on vessel Mar de Sergio | Comparing four different brands of echosounder buoys, and sampling to compare acoustic data and species composition
research icon 2016
ISSF research with IATTC in Achotines laboratory, Panama | Acoustic studies of target strength and frequency response of isolated yellowfin tuna in an offshore cage
publication icon 2016
“Towards acoustic discrimination of Tuna species at FADs” | ISSF blog post on acoustic discrimination
publication icon 2018
“Target strength of skipjack tuna (Katsuwonus pelamis) associated with Fish Aggregating Devices (FADs)” | ICES Journal of Marine Science article on acoustic identification of skipjack
publication icon 2019
“Towards acoustic discrimination of tropical tuna associated with Fish Aggregating Devices” | PLOS ONE journal article on ISSF acoustic research
publication icon 2019
In situ target strength of bigeye tuna (Thunnus obesus) associated with fish aggregating devices” | ICES Journal of Marine Science article on species identification
publication icon 2019
“Decoding the acoustic signatures of bigeye and skipjack tuna at sea could help fishers estimate the number of fish by species and size — and reduce bycatch" | ISSF blog post on acoustic discrimination
research icon 2019–Present
ISSF and AZTI research in Achotines laboratory | Development of acoustic-discrimination technology for selective fishing to reduce purse-seine catches of undersized yellowfin tuna
Acoustic Equipment Set-Up
Photo by Guillermo Boyra, © ISSF 2022
Taking acoustic measurements in the cage offshore.
Photo by Guillermo Boyra, © ISSF 2022
research icon 2022
Scientists decode yellowfin acoustic signature through Achotines research. Contrasting frequency responses have been identified for skipjack, bigeye, and yellowfin tuna.

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Learn More

publication icon ISSF Acoustic Research
“Towards acoustic discrimination of tropical tuna associated with Fish Aggregating Devices” | PLOS ONE journal article
publication icon Acoustic Discrimination Research
“Towards acoustic discrimination of Tuna species at FADs” | ISSF blog post
publication icon Reducing Bycatch
“Decoding the acoustic signatures of bigeye and skipjack tuna at sea could help fishers estimate the number of fish by species and size — and reduce bycatch" | ISSF blog post

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